The usefulness of rigid foamed polymeric boards in a variety of applications is well known. For instance, polymeric foam boards are widely used as isulating structural members. In the past, infrared attenuating agents (IAAs) such as carbon black powdered amorphous carbon, graphite, and titanium dioxide have been used as fillers in polymeric foam boards to minimize material thermal coductivity which, in turn, will maximize insulating capability (increase R-value) for a given thickness. Thermal conductivity, k is defined as the the ratio of the heat flow per unit cross-sectional to the temperature drop per unit thickness with the US unit:       Btu    ·    in              Hr      ·              Ft        2            ·      °        ⁢                   ⁢          F      .      And the metric unit:   W      m    ·    k  
The heat transfer through an insulating material can occur through solid conductivity, gas conductivity, radiation, and convection. The total thermal resistance (R-value), R is the measure of the resistance to heat transfer, and is determined as:R=t/kWhere, t=thickness.
Japanese patent application, JP 57-147510, describes the use of carbon black in rigid polyurethane foam, and with maximum carbon black levels under 0.7 weight percent, a less than 4% reduction of K-factor is achieved.
U.S. Pat. No. 4,795,763 describes a carbon black filled foam with at least 2%, preferably 2 to 10% by weight of carbon black. The carbon black has a mean particle diameter of from about 10 to 150 nanometers. The K-factor of the foam is reduced by at least about 5%.
More recently, U.S. Pat. No. 5,679,718 disclosed an evacuated, open cell, microcellular foam containing an infrared attenuating agent to provide a greater proportional reduction in foam thermal conductivity. The '718 patent discusses a mostly open cell, about 90 percent or more, and small cell, less than 70 micrometers, polymer foams. The infrared attenuating agent comprises carbon black, and graphite at about 1 to 20 weight percent based upon polymer weight.
WO 90/06339, relates to styrene polymer foam containing carbon black 1 to 20 weight percent which having a particle size of from 10 to 100 nanometers and a surface area of 10-15,000 m2/g, wherein the foam is expanded or molded expanded particles.
All of the above patents teach foams having decreased thermal conductivity. However, carbon black is a thermal conductive material, thus the thermal conductivity of the carbon black-filled foams may be increased with high loading of the carbon black. Further, the hydrophilic nature of carbon black makes it difficult to disperse evenly into polymer without a process aid, and results related large and open cells as well.
Rigid foamed plastic boards are extensively used as thermal insulating materials for many applications. It is highly desirable to improve the thermal conductivity without increasing the density, and/or the thickness of foam product. Particulary, the architectural community desires a foam board having a thermal resistance value of R=10, with a thickness of less than 1.8″, for cavity wall construction, to keep at least 1″ of the cavity gap clean.
Thus, there is a need to provide a polymeric foam product having decreased material thermal conductivity (K-factor) to provide a foam product with increased insulation value (R-value) without increasing the density and/or thickness of the polymeric foam product.